the vorticity of photospheric granulation scale flows and the surface dynamo n.
Download
Skip this Video
Loading SlideShow in 5 Seconds..
The vorticity of photospheric granulation-scale flows and the surface dynamo PowerPoint Presentation
Download Presentation
The vorticity of photospheric granulation-scale flows and the surface dynamo

Loading in 2 Seconds...

play fullscreen
1 / 16

The vorticity of photospheric granulation-scale flows and the surface dynamo - PowerPoint PPT Presentation


  • 138 Views
  • Uploaded on

The vorticity of photospheric granulation-scale flows and the surface dynamo. Alexei A. Pevtsov. Two Types of Dynamo. 1 – e.g. mean-field, overshoot region, interface dynamo 2 – AKA local, surface, photospheric, turbulent dynamo. Distinguishing Between Two Dynamos.

loader
I am the owner, or an agent authorized to act on behalf of the owner, of the copyrighted work described.
capcha
Download Presentation

PowerPoint Slideshow about 'The vorticity of photospheric granulation-scale flows and the surface dynamo' - jasper


An Image/Link below is provided (as is) to download presentation

Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author.While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server.


- - - - - - - - - - - - - - - - - - - - - - - - - - E N D - - - - - - - - - - - - - - - - - - - - - - - - - -
Presentation Transcript
two types of dynamo
Two Types of Dynamo

1 – e.g. mean-field, overshoot region, interface dynamo

2 – AKA local, surface, photospheric, turbulent dynamo

distinguishing between two dynamos
Distinguishing Between Two Dynamos

Mag. Flux of ARs varies

with sunspot cycle

  • AR and QS fields behave differently with
  • solar cycle
  • -QS fields have very short lifetime.

AR and QS magnetic fields may be

generated by separate dynamos.

Mag. Flux of QS does not

  • Em (active region) ~ 1-10 x 1034 erg
  • Em (network field at granule scale) ~ 1027 erg
  • Ek (granulation) ~ 3-6 x 1027 erg
  • -Helical dynamo is necessary to generate strong magnetic fields of ARs.
  • -Turbulent dynamo can amplify magnetic field only to 10-20% of kinetic energy.
  • -Numerical simulations: e.g. Cattaneo 1999; Schekochihin et al 2004.
  • -Pm>1 (in numerical simulations), Pm~ 10-6 <<1 (on the Sun)
helical or not
Helical or not ?

Chaotic

(turbulent)

Helical

  • Overshoot region (DeLuca & Gilman 1991)
  • Mean-field dynamo (Krause & Radler 1980)
  • Surface dynamo (Emonet & Cattaneo 2001)

Pevtsov & Longcope 2007

Tornado:

Hurricanes:

  • Helical dynamo should result in hemispheric preference for sign of helicity
  • Chaotic (turbulent) dynamo should show no hemispheric sign-preference for helicity.
slide5

* Sign of vorticity tends to be random in intergranular spaces

* In some cases, vorticity reverses its sign.

questions we address

Vorticity of Granular Flows.

Questions we Address
  • Does vorticity/kinetic helicty of granular flows show hemispheric preference?
  • Do we see the hemispheric helicity rule in quiet Sun magnetic fields created by surface dynamo?
slide7

QS??

QS??

slide8

25-26 Nov. 2008; HINODE

21 July 2009; NST

+ 50, 30, 0 degrees along central meridian; ~ 50” x 200”; 50 images, 30 sec cadence; G band 430.5 nm, 0.2 arc sec per pixel

+ 17, 0 degrees along central meridian

~ 180” x 180”; 50 images, 30 sec cadence;

TiO (705.7 nm), 0.1 arc sec per pixel

vorticities
Vorticities

FLCT – Fisher & Welsch, 2008

Hinode

NST at BBSO

slide14

N40W00

ASP

- Dependence of scatter on latitude

In agreement with recent modeling by Abbet, et al

conclusions
Conclusions
  • Vorticity of granualar flows is opposite in sign for granules and intergranular lanes; combined with expected Vz, it implies Hk<0 (Northern hemisphere) and Hk>0 (Southern hemisphere).
  • Averaged vorticity shows a slight hemispheric preference; however, significant st. deviation of averages makes this hemispheric dependency statistically insignificant.
  • Average current helicity proxy derived from vector magnetograms shows no hemispheric preference in sign.
  • Turbulent dynamo operating on spatial scale of granular flows is non-helical in its nature.
  • Surface magnetic field shows no hemispheric sign-preference because:
    • It was created by a non-helical surface dynamo
    • It was “recycled” by the surface dynamo numerous times and as the result, it lost its original helicity from subphotospheric dynamo.